Jimmy Kimmel is in something of an awkward spot between Jennifer Aniston and Justin Theroux, both close friends of Kimmel and his wife Molly. Over the weekend, Aniston and Theroux were separately invited to a birthday party for Kimmel's son -- but they apparently did not want to cross paths.

Theroux reportedly exited the party as soon as Aniston arrived, according to the Daily Mail, citing a source who claimed Theroux "did look a bit nervous" upon hearing of Aniston's entrance.

"It was obvious that he was alerted to her arrival," the source said.

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Justin Theroux out and about

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Justin Theroux out and about

NEW YORK, NY - AUGUST 14: Justin Theroux attends the INTERSECT by Lexus Preview Event on August 14, 2018 in New York City. (Photo by Jamie McCarthy/Getty Images for INTERSECT by Lexus )

NEW YORK, NY - MAY 07: Justin Theroux attends the Heavenly Bodies: Fashion & The Catholic Imagination Costume Institute Gala at The Metropolitan Museum of Art on May 7, 2018 in New York City. (Photo by Jamie McCarthy/Getty Images)

NEW YORK, NY - MAY 07: Justin Theroux attends the Heavenly Bodies: Fashion & The Catholic Imagination Costume Institute Gala at The Metropolitan Museum of Art on May 7, 2018 in New York City. (Photo by Frazer Harrison/FilmMagic)

NEW YORK, NY - MAY 01: Actor Justin Theroux and Amy Sedaris are seen taking a cab in noho on May 1, 2018 in New York City. (Photo by Raymond Hall/GC Images)

NEW YORK, NY - APRIL 10: Actor Justin Theroux is seen biking in Soho on April 10, 2018 in New York City. (Photo by Raymond Hall/GC Images)

NEW YORK, NY - APRIL 02: Justin Theroux on April 2, 2018 in New York City. (Photo by Gotham/GC Images)

PARIS, FRANCE - MARCH 06: Justin Theroux attends the Louis Vuitton show as part of the Paris Fashion Week Womenswear Fall/Winter 2018/2019 on March 6, 2018 in Paris, France. (Photo by Bertrand Rindoff Petroff/Getty Images)

PARIS, FRANCE - MARCH 05: Actor Justin Theroux is seen on March 5, 2018 in Paris, France. (Photo by Marc Piasecki/GC Images)

PARIS, FRANCE - MARCH 05: Actor Justin Theroux is seen on March 5, 2018 in Paris, France. (Photo by Marc Piasecki/GC Images)

NEW YORK, NY - FEBRUARY 12: Actor Justin Theroux is seen walking in Soho on February 12, 2018 in New York City. (Photo by Raymond Hall/GC Images)

NEW YORK, NY - FEBRUARY 08: Actor Justin Theroux attends the Adam Selman front row during New York Fashion Week: The Shows at Gallery I at Spring Studios on February 8, 2018 in New York City. (Photo by John Lamparski/Getty Images for New York Fashion Week: The Shows)

NEW YORK, NY - NOVEMBER 30: Justin Theroux attends an evening honoring Louis Vuitton and Nicolas Ghesquiere at Alice Tully Hall at Lincoln Center on November 30, 2017 in New York City. (Photo by Noam Galai/WireImage)

NEW YORK, NY - OCTOBER 25: Actor Justin Theroux is seen on October 25, 2017 in New York City. (Photo by UMV/Star Max/GC Images)

NEW YORK, NY - SEPTEMBER 19: Justin Theroux is seen on the set of 'Good Morning America' on September 19, 2017 in New York City. (Photo by Raymond Hall/GC Images)

NEW YORK, NY - SEPTEMBER 19: Actor Justin Theroux leaves the 'Good Morning America' taping at the ABC Times Square Studios on September 19, 2017 in New York City. (Photo by Ray Tamarra/GC Images)

NEW YORK, NEW YORK - JUNE 01: (L-R) Carrie Coon, Justin Theroux and Amy Brenneman attend the 'The Leftovers' FYC New York Screening at Metrograph on June 01, 2017 in New York City. (Photo by Mike Coppola/Getty Images)

NEW YORK, NY - MAY 30: Justin Theroux at Good Morning America on May 30, 2017 in New York City. (Photo by Gotham/GC Images)

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Kimmel officiated Aniston and Theroux's top-secret 2015 wedding, and he and his wife were among the close friends invited to join the couple on their Bora Bora honeymoon trip. The two couples as well as Howard Stern and his wife Beth were known to often all vacation together.

Despite the tension, it was a very happy occasion at the Kimmel household: The party was for the first birthday of son Billy, who underwent open heart surgery at just three days old at this time in 2017.

Aniston and Theroux announced their breakup in February.

27PHOTOS

Justin Theroux and Jennifer Aniston together

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Justin Theroux and Jennifer Aniston together

HOLLYWOOD, CA - JULY 26: Jennifer Aniston and Justin Theroux attend the ceremony honoring Jason Bateman with Star On The Hollywood Walk Of Fame on July 25, 2017 in Hollywood, California. (Photo by JB Lacroix/WireImage)

HOLLYWOOD, CA - JULY 26: Jennifer Aniston and Justin Theroux attend the ceremony honoring Jason Bateman with Star On The Hollywood Walk Of Fame on July 25, 2017 in Hollywood, California. (Photo by JB Lacroix/WireImage)

NEW YORK, NY - NOVEMBER 16: Justin Theroux and Jennifer Aniston attend the Celebrity Charades Goes Medieval Gala 2015 at Capitale on November 16, 2015 in New York City. (Photo by Randy Brooke/WireImage)